The present invention relates generally to fastening arrangements for securing a member to a threaded bolt or shank in self-locking relation, and more particularly to a novel self-locking fastening arrangement wherein a threaded bore having a blind end is formed in a member and receives a resilient insert configured to effect self-locking between the interengaging threads of the bore and a threaded bolt or shank when inserted a predetermined distance into the bore.
It is a conventional practice in the assembly of various machine parts and the like, and particularly in fastening various components in assembled relation, to form a blind tapped bore in a member for receiving and connection to a threaded bolt or shank. To prevent inadvertent release of the threaded bolt or shank from the threaded bore, it is common practice to employ a lock washer between opposed surfaces of the connected parts, such as between the head of a bolt and the surface periphery of the threaded bore, so as to put the interengaging threads in an axially loaded condition. When employing nuts and bolts to connect two or more parts together, the lock washer is generally interposed between the nut and an opposed surface so as to prevent inadvertent loosening or release of the nut from the associated bolt. An alternative to the use of external lock washers is to provide means internally of a nut or within a threaded blind bore to effect self-locking with a threaded shank or bolt. This approach eliminates the use of externally visible lock washers and is thus less obtrusive where cosmetic appearance is a factor. Examples of the latter type of locknuts are disclosed in U.S. Pat. Nos. 571,067, 2,410,444, 3,445,559 and 4,781,505.
U.S. Pat. No. 3,445,559 discloses a method of making a self-locking nut wherein a high-dielectric body carries a corrosion-resistent metallic sheath insert which defines the internal threads of the nut. A shroud of dilatant material is formed within the molded body as an extension of the internally threaded sheath, and serves to grip a threaded stud and resist rotative movement after assembly of the nut onto the stud. One embodiment of the nut disclosed in Pat. No. 3,445,559 forms the shroud as a full-covering cap engaged by the end of the threaded stud so that the shroud is compressed by the end of the stud and I4 forced tightly against the stud to cause a gripping action resistent to removal or loosening of the nut by ordinary vibration and the like. A significant drawback in the latter described arrangement is that the dilatant shroud completely fills the blind end of the nut bore so that tightening the nut onto a threaded stud may compress the dilatant shroud to an extent that hydraulic pressures are created which can cause male thread breakage on the stud, fracture of the associated nut body, or compression of the shroud beyond its elastic limit so that it takes a permanent set. The latter results in loss of the locking characteristics of the nut after initial usage and thereby greatly limits re-use of the nut.
The present invention addresses the aforedescribed problems in known prior self-locking nuts and the like.